This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application 2000-294919 filed on Sep. 27, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a variable valve timing system of an internal combustion engine. More particularly, the present invention pertains to a variable valve timing system for controlling the opening and closing timing of an intake valve and an exhaust valve of an internal combustion engine.
A known variable valve timing system is disclosed in Japanese Patent Laid-Open Publication No. HS1-223112 published on Aug. 17, 1999. The disclosed variable valve timing system includes a housing member rotating as a unit with a crankshaft (or a camshaft) of the internal combustion engine, and a rotor member rotating as a unit with the camshaft (or the crankshaft). The rotor member is rotatably assembled on a shoe portion provided at the housing member and forms an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member. The variable valve timing system also includes a relative rotation controlling mechanism actuated in response to supply and discharge of the operation fluid. The relative rotation controlling mechanism allows the relative rotation of the housing member and the rotor member under an unlock condition and restricts the relative rotation of the housing member and the rotor member at a lock phase between a most advanced angle phase and a most retarded angle phase, excluding the most retarded angle phase (or the most advanced angle phase), under a lock condition. The variable valve timing system further includes a fluid pressure circuit for controlling the operation fluid to be supplied to and discharged from the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism.
In this variable valve timing system, the relative rotation controlling mechanism is adapted to restrict the relative rotation of the housing member and the rotor member at the lock phase as an intermediate angle phase between the most advanced angle phase and the most retarded angle phase until the pressure of the operation fluid supplied from the fluid pressure circuit reaches a high enough pressure (i.e., until the relative rotation of the housing member and the rotor member can be maintained by the pressure of the operation fluid) when the internal combustion engine is started. If the relative rotation controlling mechanism is effectively operated at the starting of the internal combustion engine, the rotor member is not unnecessarily rotated relative to the housing member by torque fluctuations affecting the camshaft, and the occurrence of a hitting sound can be prevented. In addition, the appropriate and predetermined variable valve timing can be obtained for starting, thus improving the starting ability of the internal combustion engine.
When the housing member is integrally rotated with the crankshaft and the rotor member is integrally rotated with the camshaft with the above-described relative rotation controlling mechanism, the rotor member receives a large force to the retarded angle side relative to the housing member by the torque fluctuation affecting the camshaft. Thus when the relative rotation phase (designated in accordance with the condition when the internal combustion engine is stopped) of the housing member and the rotor member is positioned at the most advanced angle phase before the starting of the internal combustion engine, the relative rotation controlling mechanism is effectively operated as soon as the internal combustion engine is started and restricts the relative rotation of the housing member and the rotor member at the lock phase (intermediate advanced angle) as shown in FIG. 6 of the aforementioned published application. However, when the relative rotation phase of the housing member and the rotor member is positioned at the most retarded angle phase before the starting of the internal combustion engine, the relative rotation controlling mechanism requires a long time to be effectively operated after the combustion engine is started as shown in FIG. 7 of the aforementioned published application. The torque fluctuation torque caused by the cam rotates the camshaft toward the advanced angle side and toward the retarded angle side alternately. However, the torque fluctuation toward the retarded angle side is larger than toward the advanced angle side. The camshaft is thus finally rotated to the retarded angle side. Accordingly, when the relative rotation phase of the housing member and the rotor member is positioned at the most retarded angle phase before the starting of the internal combustion engine, the relative rotation controlling mechanism requires a long time to be effectively operated (or cannot be effectively operated) at the starting of the internal combustion engine. Thus, a hitting sound might occur and the starting ability of the internal combustion engine might be adversely affected.
The above described difficulties or defects might also occur when the above relative rotation controlling mechanism restricts the relative rotation of the housing member and the rotor member at the most advanced angle phase. In addition, when the housing member is integrally rotated with the camshaft and the rotor member is integrally rotated with the crankshaft, the housing member receives a large force to the retarded angle side relative to the rotor member by the torque fluctuation affecting the camshaft. Thus, under this condition and when the relative rotation phase of the housing member and the rotor member is positioned at the most advanced angle phase before the starting of the internal combustion engine, the relative rotation controlling mechanism requires a long time to be effectively operated at the starting of the internal combustion engine. Thus, a hitting sound might occur and the starting ability of the internal combustion engine might be adversely affected. The above described defects happen significantly when, for example, the friction is high under a low temperature.
A need thus exists for an improved variable valve timing system which is not as susceptible to the disadvantages and drawbacks discussed above.
According to one aspect of the present invention, a variable valve timing system for an internal combustion engine includes a housing member rotating as a unit with either a crankshaft or a camshaft of the internal combustion engine, and a rotor member relatively rotatably assembled on a shoe portion provided at the housing member and forming an advanced angle chamber and a retarded angle chamber at a vane portion in the housing member, with the rotor member rotating as a unit with either the camshaft or the crankshaft of the internal combustion engine. A relative rotation controlling mechanism is actuated in response to the supply and discharge of an operation fluid, and allows relative rotation of the housing member and the rotor member under an unlock condition while restricting relative rotation of the housing member and the rotor member at a lock phase between a most advanced angle phase and a most retarded angle phase, excluding the most retarded angle phase or the most advanced angle phase, under a lock condition. A fluid pressure circuit controls the operation fluid to be supplied to and discharged from the advanced angle chamber, the retarded angle chamber, and the relative rotation controlling mechanism. An auxiliary controlling mechanism is actuated in response to the operation fluid supplied to and discharged from the fluid pressure circuit, and allows relative rotation of the housing member and the rotor member under the unlock condition, and restricts the rotation of the rotor member to the retarded angle side or to the advanced angle side relative to the housing member at a set phase between the most retarded angle phase or the most advanced angle phase and the lock phase under the lock condition.
A biasing device is preferably provided for rotatably biasing the rotor member to the advanced angle side (or to the retarded angle side) relative to the housing member with a predetermined biasing force. The auxiliary controlling mechanism is preferably integrally assembled in the relative rotation controlling mechanism.
According to the variable valve timing system of this invention, at an early stage of the internal combustion engine starting, the operation fluid is not sufficiently discharged from the fluid pressure circuit to each advanced angle chamber, each retarded angle chamber, the relative rotation controlling mechanism, and the auxiliary controlling mechanism. Thus, the relative rotation phase of the rotor member to the housing member cannot be maintained by the pressure of the operation fluid. If the relative rotation phase of the rotor member and the housing member is not positioned at the lock phase, the housing member and the rotor member are relatively rotated by the torque fluctuation affecting to the camshaft.
The auxiliary controlling mechanism restricts the rotation of the rotor member only to the retarded angle side (or to the advanced angle side) relative to the housing member at the set phase between the most retarded angle phase (or the most advanced angle phase) and the lock phase under the lock condition. Accordingly, when the relative rotation phase of the housing member and the rotor member is varied from the most retarded angle phase (or the most advanced angle phase) to the set phase by the torque fluctuation affecting the camshaft, the auxiliary controlling mechanism comes into the lock condition. Then the auxiliary controlling mechanism restricts the rotation of the rotor member only to the retarded angle side (or to the advanced angle side) relative to the housing member, and the initial value of the relative rotation phase is held at the set phase.
Thus the relative rotation phase of the housing member and the rotor member is instantly varied to the lock phase afterwards by the torque fluctuation affecting the camshaft. Then, the relative rotation phase of the housing member and the rotor member is restricted at the lock phase by the relative rotation controlling mechanism. Accordingly, the time required for the relative rotation of the housing member and the rotor member to be restricted at the lock phase from the point of the internal combustion engine starting by the relative rotation controlling mechanism can be reduced. The occurrence of a hitting sound by the vane touching or contacting the projection is thus decreased and difficulties associated with the starting ability of the internal combustion engine can be reduced.
When the biasing device is provided for rotatably biasing the rotor member to the advanced angle side (or to the retarded angle side) relative to the housing member with a predetermined biasing force, the relative rotation of the housing member and the rotor member is varied to the advanced angle side (or to the retarded angle side) by the biasing force of the biasing device in addition to the torque fluctuation affecting the camshaft. Thus, the time required for the relative rotation of the housing member and the rotor member to be restricted at the lock phase from the point of the internal combustion engine starting by the relative rotation controlling mechanism can be further reduced. If the auxiliary controlling mechanism is integrally assembled in the relative rotation mechanism, the auxiliary controlling mechanism can be simply configured and the cost can be reduced.